The preparation of vitamin D and its derivatives are historically addressed using different strategies. One, called classical pathway, is a linear synthesis employing as starting material a steroid (such as cholesterol) which after being hydroxylated at certain positions of the tetracycle and in the side chain (C-1 and C-25), it becomes a diene steroid Δ5-7(1α,25-dihydroxy-7-dehydrocholesterol) that, by irradiation with ultraviolet light, becomes the 1α, D3 25-dihidroxiprevitamina that evolves by heating to 1α,25-dihydroxyvitamin D3. This photochemical-thermal process has low efficiency, due to the difficulties of preparing 7-dehydrointermediate performance and low photochemical process; and although some have already been optimized conditions, such as the wavelength of irradiation, filters and additives, it was only possible to obtain vitamin D in 47% yield. (M F, Brehm, J M, Alcorn, J F, Holguín, F, Aujla, S J, Celedón, J C (2005). “The Vitamin D Epidemic and its Health Consequences”. Journal of Nutrition 135 (11): 2739S-2748S).

Further, this linear path requires complete synthesis start growing for each derivative of vitamin synthesis desired, and also these modifications in the structure leads to an increase in the number of steps and a decrease in overall performance.
Another common route is the convergent synthesis which uses as starting material a transhydrindane functionalized, known as Inhoffen-Lythgoe diol, which is the synthetic precursor bicycle CD with the side chain. The Inhoffen-Lythgoe diol is obtained by reductive ozonolysis of vitamin D2. Vitamin D2 turn is obtained from ergosterol, a steroid of plant origin. (Holick M F et al, (2005). “The Vitamin D Epidemic and its Health Consequences”. Journal of Nutrition 135 (11): 2739S-2748S).
The preparation of vitamin D by total synthesis was also addressed. Overall, total synthesis strategies have addressed the synthesis of Inhoffen-Lythgoe diol, by synthetic routes using starting materials from various sources (acyl compounds, natural chiral compound “chiral pool”, etc.), with highly stereoselective stages and a variable number of stages. Illustrative examples, listed below, correspond to the obtaining of Inhoffen-Lythgoe diol, except (d), in which the vitamin is prepared.    (a) Chapleo, C. B. et al, J. Chem. Soc., Perkin Trans. 1 1977, 1211-1218. Calciferol and Its Relatives. Part 19. Synthetic Applications of Cyclic Orthoesters: Stereospecific Synthesis of a Bicyclic Alcohol Related to the Vitamins D. Starting material: (S)-(−)-3-methylbutyrolactone, 13 steps, overall yield: 4%.    (b) Trost, B. M. el al, J. Am. Chem. Soc. 1979, 101, 4378-4380. A Stereocontrolled Approach Toward Vitamin D Metabolites. A Synthesis of the Inhoffen-Lythgoe Diol. Starting material: 3-carboxytricyclo[2.2.1.02,6]heptan-5-one, 11 steps, overall yield: 3%.    (c) Johnson, W. S. et al, J. Am. Chem. Soc. 1984, 106, 1138-1139. Asymmetric Synthesis via Acetal Templates. 6. A Stereoselective Approach to a Key Intermediate for the Preparation of Vitamin D Metabolites. Starting material: 8-bromo-6-methyl-oct-5-en-1-ine, 11 steps, overall yield: 14%.    (d) Stork, G. et al, Pure Appl. Chem. 1992, 64, 1809-1812. A Total Synthesis of Calcitriol. Starting material: 4-bromobutyraldehyde, 11 steps, overall yield: approx. 10%.    (e) Hatakeyama, S. et al, J. Chem. Soc., Chem. Commun. 1989, 1893-1895. Enantioselective Synthesis of a CD-Ring Synthon for the Preparation of Vitamin D3 Metabolites. Starting material: cyclopropyl methyl ketone, 13 steps, overall yield: 4%.    (f) Brandes, E. et al, J. Chem. Soc., Chem. Commun. 1988, 500-502. Diastereoselection in an Aqueous Diels-Alder Reaction: a Formal Total Synthesis of the Inhoffen-Lythgoe Diol. Starting material: sodium (R)-(−)-methyl-3-hydroxypropionate, 20 steps, overall yield: 15%.    (g) Sikervar, V.; Fuchs, P. L. Org. Lett. 2012, 14, 2922-2924. Starting material: (S)-3-(phenylsulfonyl)-2,4-cyclohexadiene-1-ol, 12 steps, overall yield: 19%.
Although there are examples where vitamin D by fully chemical processes is prepared, these are still not very versatile and for each modification required in the substituents or in the stereochemistry of the same design should address and a new synthetic route to solve each particular approach.